18,345 research outputs found
Z_p scalar dark matter from multi-Higgs-doublet models
In many models, stability of dark matter particles is protected by a
conserved Z_2 quantum number. However dark matter can be stabilized by other
discrete symmetry groups, and examples of such models with custom-tailored
field content have been proposed. Here we show that electroweak symmetry
breaking models with N Higgs doublets can readily accommodate scalar dark
matter candidates stabilized by groups Z_p with any , leading to
a variety of kinds of microscopic dynamics in the dark sector. We give examples
in which semi-annihilation or multiple semi-annihilation processes are allowed
or forbidden, which can be especially interesting in the case of asymmetric
dark matter.Comment: 10 page
The beryllium atom and beryllium positive ion in strong magnetic fields
The ground and a few excited states of the beryllium atom in external uniform
magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for
field strengths ranging from zero up to 2.35*10^9T. With changing field
strength the ground state of the Be atom undergoes three transitions involving
four different electronic configurations which belong to three groups with
different spin projections S_z=0,-1,-2. For weak fields the ground state
configuration arises from the 1s^2 2s^2, S_z=0 configuration. With increasing
field strength the ground state evolves into the two S_z=-1 configurations
1s^22s 2p_{-1} and 1s^2 2p_{-1}3d_{-2}, followed by the fully spin polarised
S_z=-2 configuration 1s2p_{-1}3d_{-2}4f_{-3}. The latter configuration forms
the ground state of the beryllium atom in the high field regime \gamma>4.567.
The analogous calculations for the Be^+ ion provide the sequence of the three
following ground state configurations: 1s^22s and 1s^22p_{-1} (S_z=-1/2) and
1s2p_{-1}3d_{-2} (S_z=-3/2).Comment: 15 pages, 7 figure
Scattering of twisted particles: extension to wave packets and orbital helicity
High-energy photons and other particles carrying non-zero orbital angular
momentum (OAM) emerge as a new tool in high-energy physics. Recently, it was
suggested to generate high-energy photons with non-zero OAM (twisted photons)
by the Compton backscattering of laser twisted photons on relativistic electron
beams. Twisted electrons in the intermediate energy range have also been
demostrated experimentally; twisted protons and other particles can in
principle be created in a similar way. Collisions of energetic twisted states
can offer a new look at particle properties and interactions. A theoretical
description of twisted particle scattering developed previously treated them as
pure Bessel states and ran into difficulty when describing the OAM of the final
twisted particle at non-zero scattering angles. Here we develop further this
formalism by incorporating two additional important features. First, we treat
the initial OAM state as a wave packet of a finite transverse size rather than
a pure Bessel state. This realistic assumption allows us to resolve the
existing controversy between two theoretical analyses for non-forward
scattering. Second, we describe the final twisted particle in terms of the
orbital helicity --- the OAM projection on its average direction of propagation
rather than on the fixed reaction axis. Using this formalism, we determine to
what extent the twisted state is transferred from the initial to final OAM
particle in a generic scattering kinematics. As a particular application, we
prove that in the Compton backscattering the orbital helicity of the final
photon stays close to the OAM projection of the initial photon.Comment: 18 pages, 4 figures; v2: expanded introduction and section 4.2 on
final orbital helicit
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